Driver assistance systems for vehicles are generally known and established. For example, radar-based transmitters and receivers are commonly used to monitor the area immediately surrounding a vehicle for obstacles. Sensors like these are used e.g. in assistance systems for parking control, distance warning, and lane departure. It is also already established that sensors such as these scan so-called monitoring areas, also known as lobes. EP 1 506 432 B2, for example, is a sensor that generates not only one but two such lobes. In the current state of technology, these are known as the main lobe and the side lobe. They are used to monitor a vehicle's “blind spot” and, by way of distinction, also the rear of the vehicle.
The disadvantage with established driver assistance systems is that they have a “focused” monitoring area without any overlap. The description of the EP 1 506 432 B2 states, for example, that because the individual lobes fail to overlap, an unmonitored dead zone or “blind spot” exists between the two lobes. In established applications, e.g. a system for monitoring a vehicle's blind spot and/or the area immediately behind the vehicle, this dead zone is of no great relevance in terms of the vehicle's operational safety. But if the aim is to monitor cross-traffic emerging to the front, the rear or the sides of a vehicle, i.e. traffic flowing at an angle, notably at right angles to the vehicle's own path, this dead zone can pose a safety risk. In particular, a solution of this kind should be able to monitor cross-traffic with a high degree of accuracy from the moment it emerges to the point where it disappears from the vehicle's path again. Current driver assistance systems are only partly capable of satisfying these criteria, as they are unable to continuously monitor cross-traffic from the point where it emerges on one side of the vehicle and passes by the front or rear, to the point where it disappears again on the other side.